In Situ Measurements of Electrodynamics Above Thunderstorms: Past Results and Future Directions

Transcription

1 In Situ Measurements of Electrodynamics Above Thunderstorms: Past Results and Future Directions Jeremy N. Thomas 1,2, Robert H. Holzworth 2, and Michael P. McCarthy 2 1. Physics Program, Bard High School Early College II, NY 2. Dept. of Earth and Space Sciences, U. of Washington Chapman Conference May 13, 2009

2 Acknowledgments Collaborators: Tim Chinowsky, John Chin, Mike Taylor, Dominique Pautet, Matt Bailey, Natalia Solorzano, Osmar Pinto, Jr. and other members of the ELAT team at INPE, Ben Barnum, Erin Lay, Victor Pasko, Mengu Cho, and Michael Kelley Funding: NSF and NASA (USA) and FAPESP (Brazil)

3 Outline I. Motivation: Are there electric fields above thunderstorms large enough to generate TLEs? II. Review of past experiments III. In situ balloon measurements Brazil Sprite Campaign IV. In situ rocket measurements Thunderstorm III Campaign 1995 V. New directions for in situ campaigns

4 What Causes TLES? EMP CG QSF Cloud QSF

5 Quick Review of Other In situ Experiments Balloons: Gish and Wait, JGR, [1950] aircraft measurements of upward directed current of 0.5 A above thunderstorms at 12 km altitude Stergis et al., J. Atmos. Terr. Phys, [1957] balloon measurements of 1.3 A at km Holzworth J. Atmos. Terr. Phys, [1981], balloon Tohoku U. Japan, Yukihiro Takahashi et al., 2006, VLF electric fields and ELVES

6 Quick Review of Other In situ Experiments Rockets ThunderLo/ThunderHi campaign from Wallops Island, VA in 1981 [Kelley et al. 1985; Holzworth et al. 1985]. Two rockets, a balloon and a rocket-borne parachute payload were flown simultaneously. The WIPP/Thunderstorm II Campaign, Wallops Island, VA : Six stratospheric balloon flights and two ionospheric rocket flights (Kintner et al., [1987]; Arnoldy and Kintner, [1989]) The Lightning Bolt Campaign, Wallops Island, VA, 2000 (NASA Flight , PI: Wygant): One ionospheric rocket flight measured dc to VLF and HF vector electric and magnetic fields, plasma density, fast electrons, and optical power (see Rowland et al., [2004]).

7 The Sprite Balloon Campaign Brazil HV Probes vector search coil DC/AC Vector E-field (0 to 200V/m) polar conductivity DC/AC Magnetic Field up/dn Optical Power up/dn X-rays External air Temperature 3MBPS digital telemetry low voltage probes

8 Nearby (< 75 km) Quasi-Electrostatic Field Changes due to Lightning [Thomas et al., IEEE TGRS, 2004; Thomas et al. GRL, 2005; Holzworth et al. GRL, 2005; Thomas et al. Atm. Res., 2009] Flight 1 Trajectory and BIN CGs 38 electric field changes greater than 10 V/m were measured above 30km in alt. Location of strokes: Brazilian Integrated Ground Based Lightning Network (BIN) Sprites not ruled out, although none were confirmed optically

9 GOES8 Satellite IR image from 23:45 UT Dec. 6, 2002 for the southeast of Brazil

10 80 minutes of vertical dc electric field data during Flight 1 -CGs +CGs, ICs

11 Case Study: A Large +CG Event Two positive cloud-to-ground (+CG) strokes 140ms apart 34 km hor. distance from the balloon payload (alt=34km) Charge moment: C-km estimated from remote ELF (extremely low frequency) magnetic field measurements (M. Sato) ELF Data from Syowa, Antarctica

12 DC Electric Field Change Driven by +CG (Possible Sprite Event) 101V/m tau ~ 5 s tau ~ 10s 80 V/m 10 s of data In-situ data: Two lightning events, +15kA and +53kA (436 C-km), at ~00:00:09 UT Dec. 7 both less than 40 km from the balloon payload.

13 Vertical Electric Field for +CG 2 sec data model

14 model 2 sec data Radial Electric Field For +CG

15 Breakdown Thresholds

16 Model Output: Predicted lightning-driven electric fields at sprite altitudes (Z=50-80km)

17 Model Output: Predicted lightning-driven electric fields at sprite altitudes (Z=70km) 69 ms Electron conductivity dependent on lightning-driven E-field

18 Model Output: Vertical electric field vs. altitude at R=0 km

19 Thunderstorm-III Rocket Sept [Barnum, PhD Thesis,1999; Thomas et al., JGR, 2008]

20 Thunderstorm-III Payload

21

22

23 Predicted Field at ELVE Altitudes for 100 ka CG

24 New Directions for in situ measurements: Lightweight Balloon Platforms Double Langmuir probe vector electric field sensor. Student built balloon payloads launched from Moses Lake, WA A model of the speaker electric field mill.

25 New Directions for in situ measurements: Rockoon (Rocket Launched from Balloon) Rocket carried to middle atmosphere by balloon. Small and low-cost rocket launched from about 30 km and capable of reaching km in altitude First flights Van Allen Courtesy of NASA

26 Conclusions: Brazil Balloons and Thunderstorm III Rocket Balloon measurements at 35 km generally agree with quasi-static electric field model for sprites Rocket measurements at km are more than 10 times smaller than predicted by electromagnetic model for ELVEs Better understanding of conductivity in the middle atmosphere is central to understanding TLEs Additional in situ measurements needed during confirmed sprite and elve events to verify generation mechanisms